1. Field of the Invention
This invention relates to an alternator for a vehicle.
2. Description of the Related Art
In a prior-art inner-fan-type alternator for a vehicle, a fan is provided on a rotor end face located radially inward of ends of armature windings projecting at opposite sides of a fixed iron core, and an air flow generated by the fan cools the ends of the armature windings. In the prior-art inner-fan-type alternator, the spacing between the fan and the ends of the armature windings is relatively narrow, and hence fan noise tends to be caused by a wind pressure which builds there and which is generated by fan blades.
In the prior-art inner-fan-type alternator, as shown in FIGS. 18 and 19, a group of the ends of the armature windings has a ruggedness (roughness) with a constant pitch which extends along a circumferential direction and which is caused by the interference between winding phases. Thus, the prior-art inner-fan-type alternator has the problem noise having a given audible frequency is generated. In addition, the prior-art inner-fan-type alternator has the problems that the overall fan noise and the pitch noise components are relatively great. The fan noise overall is abbreviated to the OA.
Japanese published examined patent application 4-24939 discloses that gaps extending in radial directions are formed between coil ends of units of respective phases provided in stator slots, and a cooling wind generated by a cooling fan flows along a circumferential direction.
Japanese published unexamined patent application 55-157948 discloses that at least two divided coils are provided in each of phases and are inserted into a slot. Thus, ruggedness in inner circumferential surfaces of the slot is reduced.
Japanese published unexamined patent application 4-79742 discloses a winding arrangement designed so that the ruggedness of a coil end group formed by two sets of three-phase armature windings will have unequal pitches.
In each of the above-mentioned prior-art structures, the inner circumferential surfaces formed by the coil end group is uneven, and the coil ends are not spaced so that they act as an interference body with respect to a cooling wind generated by the fan. Thus, rises and drops, that is, breathing conditions, occur in the pressure of a cooling wind, and a reduction of fan noise is insufficient.
In the structure disclosed by Japanese published examined patent application 4-24939, radial-direction spacings are maintained only at a pitch such that a group of three-phase coil ends is set as one unit. Thus, interference is insufficiently suppressed.
In the structure disclosed by Japanese published unexamined patent application 55-157948, the interference noise tends to be insufficiently suppressed while the ruggedness of the inner circumferential surfaces of the coil can be reduced.
In the structure disclosed by Japanese published unexamined patent application 4-79742, the frequency of the audible noise can be varied by changing the arrangement pitch of the ruggedness. The structure disclosed by Japanese published unexamined patent application 4-79742 tends to insufficiently reduce the noise caused by the interference.
There is a method of reducing fan noise by increasing the size of an alternator while decreasing the size of a cooling fan. According to this method, the cooling performance of the fan is reduced while the size of the alternator is increased.